When an oil or gas well is completed, it is common practice to cement the well casing into the well. The casing is then perforated to allow fluid from the producing formations to flow into the well bore.
In order to increase the productivity of oil and gas wells, producing formations are sometimes treated by hydraulic fracing and acidizing. Hydraulic treading fluid is pumped into the well bore and exits through the perforations in the casing into the formation.
If some of the perforations are blocked by sediment, or if part of a formation has a lower permeability, part of the formation may not have been treated by fracing. To insure that this does not happen, perforation sealer balls are introduced into the frac fluid. The sealer balls seal the open perforations, thus forcing the treating fluid to flow through the other perforations. Thus, ball injectors have been used in the well service industry as a means of selectively diverting acidizing or fracing fluid to all of a well's perforations.
Several different types of devices have been devised for injecting such balls into a well. These devices must be capable of withstanding the high pressures of the well bore. The devices must also be able to easily and accurately count the number of balls inserted into the well. Sometimes several hundred balls are used, so at times it is very difficult to keep track of the number of balls that have been inserted. It is important that an exact count of balls be accurate at all times.
Prior versions of ball injectors have been used to inject balls into a flowline, in which a mechanical or electrical crank rotates the ball injector device. The ball counting in these versions is handled by a mechanical reed-type switch that engages a cam. The cam thus rotated with the motor shaft. The rotating plate at the bottom had four holes, dropping four balls per one full revolution. The cam had four lobes, thus causing the switch to make a count for each ¼ turn. However, prior versions could not be used, for example, if the operator wished to drop eight balls per full revolution. This resulted from problems such as the inability to readily remove the cam from the device.